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	<h1 id="firstHeading" class="firstHeading" lang="en">Gamma</h1>
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		<div id="siteSub" class="noprint">From PanoTools.org Wiki</div>
		
		
		
		
		
		
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<b>Gamma</b> is the relation between pixel value respectively electric power and visible brightness on a specific output medium. 
</p><p>Although for common uses the <b>gamma</b> value just controls the subjective brightness of the mid range
of pixels, there are certain situations in a photo stitching workflow where it makes a quantitative difference
to the results:
</p>
<ul><li>Pixel values are interpolated when correcting TCA (transverse <a href="Chromatic_aberration.html" title="Chromatic aberration">chromatic aberration</a>).</li>
<li>Pixel intensity is scaled when correcting <a href="Vignetting.html" title="Vignetting">vignetting</a>.</li>
<li>Pixel values are interpolated when photos are re-projected into the output image.</li>
<li>Blending via feathering, <a href="Enblend.html" title="Enblend">enblend</a> or smartblend<a class="external" href="https://wiki.panotools.org/Smartblend">[*]</a> averages pixel values between images.</li></ul>
<p>In any of these situations, it may be necessary to work with linear data (gamma = 1.0) or to use tools that
work internally with gamma corrected data like so:
</p><p>When using <a href="Fulla.html" title="Fulla">fulla</a> to correct chromatic aberration and vignetting, be sure to set the <b>-i</b> parameter to
the gamma of your input images.
</p><p><a href="Nona.html" title="Nona">nona</a>, <a href="PTStitcher.html" title="PTStitcher">PTStitcher</a> and <a href="PTmender.html" title="PTmender">PTmender</a> all accept a <b>g</b> (gamma) parameter on the <b>m</b> line, most
GUI front-ends<a class="external" href="https://wiki.panotools.org/GUI_front-ends">[*]</a> allow you to set this.
</p><p><a href="Enblend.html" title="Enblend">enblend</a> (including version 3.0) appears to assume that input data is already gamma-corrected, so if you are
working with linear data you probably need to change to gamma = 2.2 before running enblend.
</p><p>See Helmut Dersch's article on <a rel="nofollow" class="external text" href="http://www.panotools.org/dersch/gamma/gamma.html">Interpolation and Gamma Correction</a>.
</p><p>For details see the w:gamma correction<a class="external" href="http://www.wikipedia.org/wiki/gamma_correction">[*]</a> article and the
<a rel="nofollow" class="external text" href="http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html">Gamma FAQ</a>.
</p>

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